Laplace's Demon

What is Laplace's Demon?

Laplace's demon is an hypothetical entity, proposed in 1814, that is thought to have the precise knowledge of location and momentum of every atom in the universe, thus could predict the future of the universe accurately as well as has complete knowledge about the past of the universe. It is the articulation of casual or scientific determinism, according to which if one knows the precise location and momentum of each and every atom of the universe then, the person can calculate or predict the future as well as the past of the universe through the laws of classical mechanical physics. This hypothetical being or entity was first proposed by Pierre Simon Laplace. It is to be noted that Laplace himself did not mention the word 'demon' rather he called the being 'an intellect'.

Robert Pierre Laplace

                                 

 

Laplace said :

 

 "We may regard the present state of the universe as the effect of its past and the cause of its future. An intellect which at a certain moment would know all the forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect was also vast enough to submit this data to analysis, it would embrace in a single formula the moments of the greatest bodies of the universe and those of the tiniest atoms; for such an intellect nothing would be uncertain and the future just like the past would be present before his own eyes."

Arguments

Various arguments have been made against the existence of such an intellect or entity. Scientist have give out quite a few theories and problems that occur while trying to predict future or have complete knowledge of the past. Some of the arguments are-

1. Violation of second law of thermodynamics- The second law of thermodynamics states that the entropy(disorder) of an isolated system can only increase over time. According to the argument laid out by Robert Ulanowicz, in 1996, most of the thermodynamic processes are irreversible. Since the laplace's demon is based on the process of reversibility and if thermodynamic quantities are taken to be purely physical then it is not possible to retrace the previous position or momentum of any atom or particle.
   
   
   
   
   
2. Chaos theory- It describes that how a deterministic system can exhibit behaviour that is almost impossible to predict and minor changes between the starting conditions of the two system can result in major differences(just like the butterfly effect). However, its argument to contradict laplace's demon is not quite applicable.                                                                                                                                      
3.  Past prediction- If we consider the theory of multiverse to be true, then in two of the alternate universes, with same laws of physics, with a similar present there can be two different pasts. Simply it can be said that two different initial conditions of two diffrent system can result in a similar present condition of both the system. Thus it is very unlikely for laplace's demon to predict both the past distinctly.

Is  Laplace's Demon a possibility?

Scientists gave various arguments denying the existence or possibility of existence of such an intellect, however, the chaos theory argument dost not actually contradict the possibility of this intellect as the information about the current position and forces and momenta of the atoms is to infinite precision, while the chaos theory is applicable when the knowledge of system is imperfect. Similar can be said for past prediction problems as broadly the variables and conditions of the two system might seem similar but since the information is infinitely precise the microscopic variables will have different variables thus it is possible to retrace the past. The violation of second law of thermodynamics does not completely hold as there are thermodynamic reversible processes thus there can be constant entropy. 

Practicality of Laplace's Demon

                                     

If suppose the existence of such an intellect is possible and humans at some point of time in the near future are able to gather the information about every existing atom in the universe to infinite precision  then it will require huge amount of computational power to analyse the information and further predict the future or the past. If somehow we are even able to achieve such computational power then the productivity of such an intellect would be very low; that is to say that the ratio of the amount of time taken to predict the future and the amount of predicted time in future would be very high. For example, it would take almost 100 years to predict 1 millisecond of the future, which obviously does not seem to be a good bargain.

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